Nanocrystal/sol-gel nanocomposites

ABSTRACT

The present invention is directed to solid composites including colloidal nanocrystals within a sol-gel host or matrix and to processes of forming such solid composites. The present invention is further directed to alcohol soluble colloidal nanocrystals useful in formation of sol-gel based solid composites.

STATEMENT REGARDING FEDERAL RIGHTS

This invention was made with government support under Contract No.W-7405-ENG-36 awarded by the U.S. Department of Energy. The governmenthas certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates to nanocrystal/sol-gel composites and toprocesses of forming such nanocrystal/sol-gel composites. Additionally,the present invention relates to alcohol-soluble colloidal nanocrystals.

BACKGROUND OF THE INVENTION

Semiconductor nanocrystals (NCs), often referred to as nanocrystalquantum dots (NQDs), are of interest for their size-tunable optical andelectronic properties. Intermediate between the discrete nature ofmolecular clusters and the collective behavior of the bulk, NQDs areunique building blocks for the bottom-up assembly of complex functionalstructures. NQDs can be conveniently synthesized using colloidalchemical routes such as the solution-based organometallic synthesisapproaches for the preparation of CdSe NQDs described by Murray et al.,J. Am. Chem. Soc., 115, 8706 (1993) or by Peng et al., J. Am. Chem.Soc., 123, 183 (2001), such references incorporated herein by reference.Generally, these procedures involve an organometallic approach.Typically these chemical routes yield highly crystalline, monodispersesamples of NQDs. Because of their small dimensions (sub-10 nm) andchemical flexibility, colloidal NQDs can be viewed as tunable“artificial” atoms and as such can be manipulated into larger assembliesengineered for specific applications.

A significant challenge for obtaining stable optical properties andrealizing optical applications of quantum dots is to incorporate theNQDs into a suitable transparent host matrix. Early attempts involvedthe direct growth of the nanoparticles within glassy matrices; however,the resulting materials were plagued by poorly controlled surfacepassivation, low filling factors and large size dispersities.

More recently, researchers have sought to decouple the synthesis of thenanoparticles from the fabrication of the composites. Selvan et al.,Adv. Mater. v. 13, pp. 985–988 (2001) describe octylamine-passivatedsemiconductor quantum dots transferred into butanol prior to sol-gelprocessing with resultant volume fractions or loadings of only up toabout 0.1 percent. Sundar et al., Adv. Mater., v. 14, pp. 739–742(2002), describe incorporation of NCs wherein the surface-passivatingligands are replaced with tris(hydroxylpropyl)phosphine to stabilize theNCs in polar solvents such as ethanol and provide hydroxyl groups whichcan be reacted into a titania sol-gel matrix. Volume fractions orloadings as high as 10 to 12 percent were reported.

Despite the gradual progress, problems have remained. After long andcareful research, new approaches have now been developed for thepreparation of colloidal nanocrystal-containing composites.

It is an object of the present invention to provide new processes forpreparing solid composites including colloidal nanocrystals and toprovide the solid composites from such processes.

It is another object of the present invention to form solid compositeswith high volume loadings of the colloidal nanocrystals.

Still another object of the present invention is solid compositesincluding colloidal nanocrystals where the solid composites arecharacterized by high refractive indices.

Still another object of the present invention is the preparation ofalcohol-soluble colloidal nanocrystals including alcohol or carboxylicacid terminated groups thereon.

SUMMARY OF THE INVENTION

In accordance with the purposes of the present invention, as embodiedand broadly described herein, the present invention provides a processfor preparing a solid composite including colloidal nanocrystalsdispersed within a sol-gel host, the process including forming anadmixture of colloidal nanocrystals, a lower alcohol, a non-polarco-solvent and a sol-gel precursor material, and, forming the solidcomposite from the admixture. The present invention further provides asolid composite formed by the above process. In one embodiment, thelower alcohol is ethanol and the non-polar co-solvent istetrahydrofuran.

The present invention still further provides a process for preparing asolid composite including colloidal nanocrystals dispersed within asol-gel host matrix, the process including reacting colloidalnanocrystals passivated with hydrophobic ligands with a multi-functionalcompound of the formula X_(x)—(Z_(n))—Y_(y) where X is an amino group, athiol group, a phosphonic acid group, a phosphine oxide group, a nitrilegroup, a thiocyanate group, or a carboxylic acid group, x is an integerand is one or more, Z is a hydrocarbon group, such as an alkyl group, anaryl group or an alkylaryl group, a polyether group, an ethylene oxidegroup, a propylene oxide group or a mixture thereof, n is from 1 to 20,Y is a hydroxyl group, a carboxylic acid group, a sulfonic acid group, aphosphonic acid group, or an alkoxysilane group, and y is an integer andis one or more, within a solvent to form a homogeneous colloidalnanocrystal solution including colloidal nanocrystals with at least aportion of hydroxyl-terminated groups, carboxylic acid-terminatedgroups, sulfonic acid-terminated groups, phosphonic acid-terminatedgroups, or alkoxysilane-terminated groups thereon; admixing thehomogeneous colloidal nanocrystal solution and a sol-gel precursormaterial; and, forming the solid composite from the admixture. In oneembodiment, the multi-functional molecule is an amino-hydroxyl compoundsuch as 4-aminobutanol or 6-aminohexanol.

The present invention still further provides a solid composite that isthe reaction product of colloidal nanocrystals including at least aportion of hydroxyl-terminated groups, carboxylic acid-terminatedgroups, sulfonic acid-terminated groups, phosphonic acid-terminatedgroups or alkoxysilane-terminated groups thereon and a sol-gel precursormaterial.

The present invention still further provides alcohol-soluble colloidalnanocrystals including the reaction product of colloidal nanocrystalsand a multi-functional compound of the formula X_(x)—(Z_(n))—Y_(y) whereX is an amino group, a thiol group, a phosphonic acid group, a phosphineoxide group, a nitrile group, a thiocyanate group, or a carboxylic acidgroup, x is an integer and is one or more, Z is a hydrocarbon group,such as an alkyl group, an aryl group or an alkylaryl group, a polyethergroup, an ethylene oxide group, a propylene oxide group or a mixturethereof, n is from 1 to 20, Y is a hydroxyl group, a carboxylic acidgroup, a sulfonic acid group, a phosphonic acid group, or analkoxysilane group, and y is an integer and is one or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of a pathway by which colloidalnanocrystals can become incorporated into a sol-gel matrix.

FIG. 2 shows a digital representation of a photomicrograph of aCdSe/sol-gel solid composite formed within a microcapillary tube.Micro-ring lasing by the colloidal CdSe nanocrystals within themicrocapillary cavity was observed as the very bright spot in the centerof the tube, which was under optical excitation at 400 nm. The CdSecolloidal nanocrystals were approximately 5 nm in diameter and emittedin the red.

DETAILED DESCRIPTION

The present invention is concerned with solid composites includingcolloidal nanocrystals within a sol-gel host or matrix and withprocesses of forming such solid composites. The present invention isfurther concerned with alcohol soluble colloidal nanocrystals useful inthe formation of sol-gel based solid composites.

As used herein, the term “nanocrystal” refers to particles less thanabout 150 Angstroms in the largest axis, and preferably from about 10 toabout 150 Angstroms. Also, within a particularly selected colloidalnanocrystal, the colloidal nanocrystals are substantially monodisperse,i.e., the particles have substantially identical size and shape.

The colloidal nanocrystals are generally members of a crystallinepopulation having a narrow size distribution. The shape of the colloidalnanocrystals can be a sphere, a rod, a disk and the like. In oneembodiment, the colloidal nanocrystals include a core of a binarysemiconductor material, e.g., a core of the formula MX, where M can becadmium, zinc, mercury, aluminum, lead, tin, gallium, indium, thallium,magnesium, calcium, strontium, barium, copper, and mixtures or alloysthereof and X is sulfur, selenium, tellurium, nitrogen, phosphorus,arsenic, antimony, and mixtures or alloys thereof. In anotherembodiment, the colloidal nanocrystals include a core of a ternarysemiconductor material, e.g., a core of the formula M₁M₂X, where M₁ andM₂ can be cadmium, zinc, mercury, aluminum, lead, tin, gallium, indium,thallium, magnesium, calcium, strontium, barium, copper, and mixtures oralloys thereof and X is sulfur, selenium, tellurium, nitrogen,phosphorus, arsenic, antimony, and mixtures or alloys thereof. Inanother embodiment, the colloidal nanocrystals include a core of aquaternary semiconductor material, e.g., a core of the formula M₁M₂M₃X,where M₁, M₂ and M₃ can be cadmium, zinc, mercury, aluminum, lead, tin,gallium, indium, thallium, magnesium, calcium, strontium, barium,copper, and mixtures or alloys thereof and X is sulfur, selenium,tellurium, nitrogen, phosphorus, arsenic, antimony, and mixtures oralloys thereof. In other embodiments, the colloidal nanocrystals includea core of a quaternary semiconductor material, e.g., a core of a formulasuch as M₁X₁X₂, M₁M₂X₁X₂, M₁M₂M₃X₁X₂, M₁X₁X₂X₃, M₁M₂X₁X₂X₃ orM₁M₂M₃X₁X₂X₃, where M₁, M₂ and M₃ can be cadmium, zinc, mercury,aluminum, lead, tin, gallium, indium, thallium, magnesium, calcium,strontium, barium, copper, and mixtures or alloys thereof and X₁, X₂ andX₃ can be sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic,antimony, and mixtures or alloys thereof. In one embodiment, thecolloidal nanocrystals are of silicon or germanium. In some instances,oxides such as zinc oxide (ZnO) and the like may be used as well.Examples include cadmium sulfide (CdS), cadmium selenide (CdSe), cadmiumtelluride (CdTe), zinc sulfide (ZnS), zinc selenide (ZnSe), zinctelluride (ZnTe), mercury sulfide (HgS), mercury selenide (HgSe),mercury telluride (HgTe), aluminum nitride (AlN), aluminum sulfide(AlS), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminumantimonide (AlSb), lead sulfide (PbS), lead selenide (PbSe), leadtelluride (PbTe), gallium arsenide (GaAs), gallium nitride (GaN),gallium phosphide (GaP), gallium antimonide (GaSb), indium arsenide(InAs), indium nitride (InN), indium phosphide (InP), indium antimonide(InSb), thallium arsenide (TlAs), thallium nitride (TlN), thalliumphosphide (TlP), thallium antimonide (TlSb), zinc cadmium selenide(ZnCdSe), indium gallium nitride (InGaN), indium gallium arsenide(InGaAs), indium gallium phosphide (InGaP), aluminum indium nitride(AlInN), indium aluminum phosphide (InAlP), indium aluminum arsenide(InAlAs), aluminum gallium arsenide (AlGaAs), aluminum gallium phosphide(AlGaP), aluminum indium gallium arsenide (AlInGaAs), aluminum indiumgallium nitride (AlInGaN) and the like, mixtures of such materials, orany other semiconductor or similar materials. In another embodiment, thecolloidal nanocrystals include a core of a metallic material such asgold (Au), silver (Ag), cobalt (Co), iron (Fe), nickel (Ni), copper(Cu), manganese (Mn), alloys thereof and alloy combinations.

Additionally, the core of any semiconductor material or of any metallicmaterial can have an overcoating on the surface of the core. Theovercoating can also be a semiconductor material, such an overcoatinghaving a composition different than the composition of the core. Theovercoating on the surface of the colloidal nanocrystals can includematerials selected from among Group II-VI compounds, Group II-Vcompounds, Group III-VI compounds, Group III-V compounds, Group IV-VIcompounds, Group I-III-VI compounds, Group II-IV-V compounds, and GroupII-IV-VI compounds. Examples include cadmium sulfide (CdS), cadmiumselenide (CdSe), cadmium telluride (CdTe), zinc sulfide (ZnS), zincselenide (ZnSe), zinc telluride (ZnTe), mercury sulfide (HgS), mercuryselenide (HgSe), mercury telluride (HgTe), aluminum nitride (AlN),aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide(AlSb), gallium arsenide (GaAs), gallium nitride (GaN), galliumphosphide (GaP), gallium antimonide (GaSb), indium arsenide (InAs),indium nitride (InN), indium phosphide (InP), indium antimonide (InSb),thallium arsenide (TlAs), thallium nitride (TlN), thallium phosphide(TlP), thallium antimonide (TlSb), lead sulfide (PbS), lead selenide(PbSe), lead telluride (PbTe), zinc cadmium selenide (ZnCdSe), indiumgallium nitride (InGaN), indium gallium arsenide (InGaAs), indiumgallium phosphide (InGaP), aluminum indium nitride (AlInN), indiumaluminum phosphide (InAlP), indium aluminum arsenide (InAlAs), aluminumgallium arsenide (AlGaAs), aluminum gallium phosphide (AlGaP), aluminumindium gallium arsenide (AlInGaAs), aluminum indium gallium nitride(AlInGaN) and the like, mixtures of such materials, or any othersemiconductor or similar materials. The overcoating upon the corematerial can include a single shell or can include multiple shells forselective tuning of the properties. The multiple shells can be ofdiffering materials.

In a first process of the present invention, colloidal nanocrystals aremixed with a lower alcohol, a non-polar solvent and a sol-gel precursormaterial, and the resultant solution can be used to form a solidcomposite. For example, the solution can be deposited onto a suitablesubstrate to yield homogeneous, solid composites from the solution ofcolloidal nanocrystals and sol-gel precursor. By homogeneous, it ismeant that the colloidal nanocrystals are uniformly dispersed in theresultant product. In some instances, non-uniform dispersal of thecolloidal nanocrystals is acceptable. In some embodiments of theinvention, the solid composites can be transparent or optically clear.This first process of the present invention is a simple straight-forwardprocess for preparing such solid composites.

The lower alcohol used in this process is generally an alcoholcontaining from one to four carbon atoms, i.e., a C₁ to C₄ alcohol.Among the suitable alcohols are included methanol, ethanol, n-propanol,isopropanol, n-butanol, sec-butanol and t-butanol.

The non-polar solvent is used in the process to solubilize the colloidalnanocrystals and should be misible with the lower alcohol. The non-polarsolvent is generally chosen from among tetrahydrofuran, toluene, xyleneand the like. Tetrahydrofuran is a preferred non-polar solvent in thisprocess.

Sol-gel processes generally refer to the preparation of a ceramicmaterial by preparation of a sol, gelation of the sol and removal of thesolvent. Sol-gel processes are advantageous because they are relativelylow-cost procedures and are capable of coating long lengths orirregularly shaped substrates. In forming the sol-gel based solutionused in the processes of the present invention, suitable sol-gelprecursor materials are mixed with the other components.

Sol-gel processes can be carried out as described by Brinker et al,“Sol-Gel Science, The Physics and Chemistry of Sol-Gel Processing”,Academic Press, 1990. Among suitable sol-gel precursor materials areincluded metal alkoxide compounds, metal halide compounds, metalhydroxide compounds, combinations thereof and the like where the metalis a cation from the group of silicon, titanium, zirconium, andaluminum. Other metal cations such as vanadium, iron, chromium, tin,tantalum and cerium may be used as well. Sol solutions can be spin-cast,dip-coated, or sprayed onto substrates in air. Sol solutions can also becast into desired shapes by filling molds or cavities as well. Among thesuitable metal alkoxide compounds can be included titanium tetrabutoxide(titanium (IV) butoxide), titanium tetraethoxide, titaniumtetraisopropoxide, zirconium tetraisopropoxide, tetraethoxysilane(TEOS). Among suitable halide compounds can be included titaniumtetrachloride, silicon tetrachloride, aluminum trichloride and the like.

The sol-gel based solutions generated in this first process of thepresent invention are highly processable. They can be used to form solidcomposites in the shape of planar films and can be used to mold solidcomposites of various other shapes and configurations. In this firstprocess of the present invention, volume fractions or loadings of thecolloidal nanocrystals have been prepared as high as about 13 percent byvolume and may be as high as up to about 30 percent by volume. Further,the first process of the present invention has allowed preparation ofsolid composites with a refractive index of 1.9, such refractive indexvalues being tunable.

A second process of the present invention relies upon ligand-exchange ofsurface capping agents on semiconductor colloidal nanocrystals with amulti-functional compound of the formula X_(x)—(Z_(n))—Y_(y) where X canbe an amino (—NH₂) group, a thiol (—SH) group, a phosphonic acid(—PO₃H₂) group, a phosphine oxide (—PO) group, a nitrile group (—CN), athiocyanate group (—SCN), or a carboxylic acid group (—COOH), x is aninteger and is one or more, Z can be a hydrocarbon group, such as analkyl group, an aryl group or an alkylaryl group, a polyether group, anethylene oxide group, a propylene oxide group or a mixture thereof, ncan generally be from 1 to 20, Y can be a hydroxyl (—OH) group, acarboxylic acid (—COOH) group, a sulfonic acid (—SO₃H) group, aphosphonic acid group (—PO₃H₂) group, or a alkoxysilane group (—Si(OX))and y is an integer and is one or more.

The alkyl group can be linear or branched. With x and y being an integerof one or more, the multi-functional compound can include, e.g., morethan a single amino group, more than a single thiol group, more than asingle phosphonic acid group, more than a single phosphine oxide group,more than a single nitrile group, more than a single thiocyanate group,more than a single alkoxysilane group or combinations thereof, as X_(x)in combination with one or more of the groups represented by Y_(y).Combinations of the enumerated groups represented by X may also becombined with combinations of the enumerated groups represented by Y.For example, the multi-functional compound can include the combinationof functionalities such as amino-hydroxyl, thiol-hydroxyl, phosphonicacid-hydroxyl, phosphine oxide-hydroxyl, amino-carboxylic acid,thiol-carboxylic acid, phosphonic acid-carboxylic acid, phosphineoxide-carboxylic acid, amino-sulfonic acid, thiol-sulfonic acid,phosphonic acid-sulfonic acid, phosphine oxide-sulfonic acid,amino-phosphonic acid, thiol-phosphonic acid, and phosphineoxide-phosphonic acid. Exemplary materials include 2-aminoethanol,2-amino-1-propanol, 3-amino-1-propanol, 2-amino-1-butanol,3-amino-1-butanol, 4-amino-1-butanol, 3-amino-2-butanol,2-amino-1-phenyl-1-butanol, 6-amino-1-hexanol, p-aminobenzenesulfonicacid, 3-aminobutyric acid, 4-aminobutyric acid, 4-amino-2-hydroxybutyricacid, 1,3-diamino-2-propanol, 3-mercaptopropionic acid,4-phosphonobutyric acid, 3-aminopropyltriethoxysilane,(3-mercaptopropyl)trimethoxysilane,3-(dimethoxymethylsilyl)-1-propanethiol, 3-mercapto-1-propanol,4-mercapto-1-butanol, 6-mercapto-1-hexanol, 3-hydroxypropionitrile,6-hydroxyhexanoic acid, 4-hydroxybutylphosphonic acid,tris(hydroxypropyl)phosphine oxide, bis(dibutyl)(hydroxypropyl)phosphineoxide and the like.

The result of the ligand-exchange of surface capping agents onsemiconductor colloidal nanocrystals with the multi-functional compoundis the formation of a colloidal nanocrystal solution including colloidalnanocrystals having at least a portion of hydroxyl-terminated,carboxylic acid-terminated groups, sulfonic acid-terminated groups,siloxy-terminated groups, or phosphonic acid-terminated groups thereon.This solution is generally homogeneous.

Subsequently, upon addition of a sol-gel precursor material, thecolloidal nanocrystals can actually become part of a sol-gel matrixduring a sol-gel polymerization reaction. For example, the solution canbe deposited onto a suitable substrate to yield homogeneous, solidcomposites from the solution of colloidal nanocrystals and sol-gelprecursor. By homogeneous, it is meant that the colloidal nanocrystalsare uniformly dispersed in the resultant product. In some embodiments ofthe invention, the solid composites can be transparent or opticallyclear. Films can be prepared simply by spin-casting such a sol solutiononto a suitable substrate.

The sol-gel based solutions generated in this second process of thepresent invention are highly processable. They can be used to form solidcomposites in the shape of planar films and can be used to mold solidcomposites of various other shapes and configurations. This secondprocess can yield solid composites with very high volume loadings ofcolloidal nanocrystals (up to 20% for CdSe colloidal nanocrystals,nearly twice any previously reported values) and tunable refractiveindices (up to 2.1).

In another aspect of the present invention, the resultant product of theligand-exchange of surface capping agents on semiconductor colloidalnanocrystals with the multifunctional compounds yields an intermediateproduct of alcohol-soluble colloidal nanocrystals. Alcohol solubility isneeded for compositions that are to be reacted with sol-gel precursorswhere water soluble compositions would not be efficient. Accordingly,such alcohol-soluble colloidal nanocrystals can be subsequentlyincorporated into a sol-gel matrix in forming a solid composite. Suchalcohol-soluble colloidal nanocrystals are stable and have beensuccessfully stored for months until subsequent use. The alcohol-solublecolloidal nanocrystals can be stored in an alcohol such as ethanol ormay be stored as dry particles.

For the processes of the present invention, the colloidal nanocrystalscan include all types of nanocrystals capped with hydrophobic ligands,including, e.g., semiconductor NQDs such as cadmium sulfide (CdS),cadmium selenide (CdSe), cadmium telluride (CdTe), zinc sulfide (ZnS),zinc selenide (ZnSe), zinc telluride (ZnTe), mercury sulfide (HgS),mercury selenide (HgSe), mercury telluride (HgTe), aluminum nitride(AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminumantimonide (AlSb), gallium arsenide (GaAs), gallium nitride (GaN),gallium phosphide (GaP), gallium antimonide (GaSb), indium arsenide(InAs), indium nitride (InN), indium phosphide (InP), indium antimonide(InSb), thallium arsenide (TlAs), thallium nitride (TlN), thalliumphosphide (TlP), thallium antimonide (TlSb), lead sulfide (PbS), leadselenide (PbSe), lead telluride (PbTe), silicon (Si), germanium (Ge) andmixtures of such materials. The colloidal nanocrystals can also be metalnanoparticles such as gold (Au), silver (Ag), cobalt (Co), iron (Fe),nickel (Ni), copper (Cu), manganese (Mn), alloys thereof and alloycombinations thereof.

Each of the present processes can provide resultant films that areoptically transparent and hard. The colloidal nanocrystals are containedwithin a stable environment and the narrow size dispersity of thecolloidal nanocrystals within these materials is preserved. Of thepresent processes, the particular process employed can depend upon theultimate application of interest. That is, for applications requiringhigh volume loadings or high refractive indices, the second process canbe preferred, and for applications requiring simplicity or convenience,the first process can be preferred.

The solid composites prepared in the processes of the present inventionshow improved photostability for the colloidal nanocrystals within thesolid composite. This enhanced stability is in comparison to similarcolloidal nanocrystals not incorporated into such solid matrices orhosts. The solid composites may be useful as phosphor materials for usein, e.g., light emitting diodes and solid state lighting structures.Additionally, the solid composites demonstrate strong nonlinear opticaland optical gain properties and may be used as active waveguides fornonlinear optical switching and optical amplification. Theprocessability of the sol-gel solutions and the photostability of theresultant solid composites allow for their use as the active medium inoptical devices including optical memory devices. These types of solidcomposites can have application as the active medium in dynamicholography devices used in optical communications and opticalinformation processing. For example, all-optical switching and opticalimage correlation may be facilitated by solid composites of the presentinvention. Also, the solid composites can be the active media in solidstate lasers.

The present invention is more particularly described in the followingexamples which are intended as illustrative only, since numerousmodifications and variations will be apparent to those skilled in theart.

CdSe and (CdSe)ZnS core-shell colloidal nanocrystals were synthesized aspreviously described by Murray et al., J. Am. Chem. Soc., v. 113, 8706(1993), by Dabbousi et al., J. Phys. Chem. B, v. 101, 9463 (1997), andby Qu et al., J. Am. Chem. Soc., v. 124, 2049 (2002).

EXAMPLE 1

The colloidal nanocrystals were first isolated from their growthenvironment by several rounds of precipitation, which involvedsolubilizing the colloidal nanocrystals in hexane or chloroform and thenprecipitating the colloidal nanocrystals from these solvents withacetone or methanol. The colloidal nanocrystals were taken into an inertatmosphere dry box. For 17 milligrams (mg) of CdSe colloidalnanocrystals, 0.15 milliliter (mL) of tetrahydrofuran and 0.075 mL ofethanol were added along with 15 mg of titanium (IV) butoxide. Thesolution was stirred with heating between 40° C. and 65° C. for from 3to 6 hours, filtered, and then spin-coated onto a substrate, such as amicroscopic slide. Under these conditions, CdSe volume loadings as highas 13% have been achieved with a film refractive index of 1.9. To adjustthese values, the relative amounts of colloidal nanocrystals, solventsand titanium (IV) butoxide can be varied. This procedure is applicableto colloidal nanocrystals of a variety of shapes (spheres, rods, orother geometries) and compositions (Group II-VI compounds, Group II-Vcompounds, Group III-VI compounds, Group III-V compounds, Group IV-VIcompounds, and the like).

EXAMPLE 2

CdSe colloidal nanocrystals prepared in accordance with Qu et al. werewashed several times with acetone and methanol to remove all unboundligand. This step often causes a dramatic decrease in photoluminescence(PL) quantum yields (QYs), often to less than a third of the originalvalue. To improve the QYs, the colloidal nanocrystals were allowed tostir in octylamine overnight. The CdSe colloidal nanocrystals wereprecipitated from solution with methanol, the solvent was removed, andthe colloidal nanocrystals were taken into the inert atmosphere dry box.For 75 mg of CdSe colloidal nanocrystals, 0.1 mL of tetrahydrofuran, 0.6mL of 1-propanol, and 45–50 mg of 6-amino-1-hexanol were added. Thesolution was stirred for several minutes until the mixture washomogeneous. At this point, 45 mg of titanium (IV) butoxide was added,and the solution was allowed to stir at 60° C. for from 4 to 6 hours.The colloidal nanocrystals become incorporated into the titania sol in amanner as depicted in FIG. 1. The solution was filtered, and the filmswere prepared by spin-coating the sol onto a microscope slide. The filmswere dried in air overnight or alternatively could be dried by heatingon a hot plate stabilized at 100° C. for 1 to 2 minutes.

This procedure gave rise to nanocomposites with a refractive index of2.1 and volume loadings of CdSe colloidal nanocrystals as high as 20%.These values can be adjusted by changing the ratios of titanium (IV)butoxide and 6-amino-1-hexanol to colloidal nanocrystals. This procedureis applicable to colloidal nanocrystals of a variety of shapes (spheres,rods, or other geometries) and compositions (Group II-VI compounds,Group II-V compounds, Group III-VI compounds, Group III-V compounds,Group IV-VI compounds, and the like). In addition, while6-amino-1-hexanol was used, the procedure works with a variety of ligandheadgroups, (e.g., phosphines, thiols, phosphonic acids and the like)and a variety of amphiphilic groups including alcohols with thedescribed functionalities as well as carboxylic acids with the same. Theprocedure can be used to make silica-based solid composites in additionto the titania-based solid composites. Solvents other than 1-propanolcan be used as well, e.g., other alcohols such as ethanol, butanol, andthe like.

Although the present invention has been described with reference tospecific details, it is not intended that such details should beregarded as limitations upon the scope of the invention, except as andto the extent that they are included in the accompanying claims.

1. A solid composite comprising the reaction product of (i) colloidalnanocrystals including at least a portion of alkoxysilane-terminatedgroups thereon and (ii) a sol-gel precursor material.
 2. The solidcomposite of claim 1 wherein said colloidal nanocrystals have a volumeloading of up to about 30 percent by volume within said solid composite.3. The solid composite of claim 1 wherein said sol-gel precursormaterial is selected from the group consisting of metal alkoxidecompounds, metal halide compounds, and metal hydroxide compounds wherethe metal is selected from the group consisting of silicon, titanium,zirconium, aluminum, vanadium, iron, tin, tantalum, cerium, andchromium.
 4. The solid composite of claim 1 wherein said colloidalnanocrystals are selected from the group consisting of M₁X₁, M₁M₂X₁,M₁M₂M₃X₁, M₁X₁X₂, M₁M₂X₁X₂, M₁M₂M₃X₁X₂, M₁X₁X₂X₃, M₁M₂X₁X₂X₃, andM₁M₂M₃X₁X₂X₃, where M₁, M₂, and M₃ are each selected from the groupconsisting of Zn, Cd, Hg, Al, Ga, In, Tl, Pb, Sn, Mg, Ca, Sr, Ba,mixtures and alloys thereof and X₁, X₂, and X₃ are each selected fromthe group consisting of S, Se, Te, As, Sb, N, P, mixtures and alloysthereof, Si, Ge, Au, Ag, Co, Fe, Ni, Cu, Mn and alloys of Au, Ag, Co,Fe, Ni, Cu, Mn or alloy combinations thereof.